This invention relates to an improved data transmission system which is not prevented from performing accurate transmission by a load connected between both ends of transmission wirings or lines.
Generally data transmission wirings, particulary, using power wirings as service wirings are operated with a parallel signal input method. When a low impedance load is connected between both ends of power wirings, signals can not be transmitted because of a decrease in the receiving level.
FIG. 1 shows a circuit diagram of a general data transmission system using the parallel signal input method. The general transmission system comprises transmission wirings or lines 1, a transmitting station 2 (where E.sub.S is a transmitting output voltage and Z.sub.S is an output impedance of the transmitting station 2), a receiving station 3 (where Z.sub.R is an input impedance of the receiving station 3), loads 4 and 5 (where Z.sub.LS and Z.sub.LR are impedances of loads 4 and 5, respectively).
A receiving voltage E.sub.R can be expressed by the following equation. ##EQU1## Further, if Z.sub.LS &gt;&gt;Z.sub.LR, the receiving voltage E.sub.R is given by the following equation in view of equations (1) and (2). ##EQU2## Accordingly, signals can not receive on the receiving station by using the voltage E.sub.R when Z.sub.LR .apprxeq.0. But, because a transmission current I.sub.S .apprxeq.0, a receiving current I.sub.R is given as follows: ##EQU3## where the transmission current I.sub.R is maximum. Accordingly, signals can receive on the receiving station by using the current I.sub.R.
But, when Z.sub.LS .apprxeq.0, the receiving current I.sub.R and the transmission current I.sub.S and the receiving voltage E.sub.R are given as follows: EQU I.sub.S =I.sub.R .apprxeq.0, E.sub.R .apprxeq.0 (4)
Effective signals for transmitting data are not applied on the transmitting wirings or lines 1 by using either current I.sub.R or the voltage E.sub.R.